Method, device and system for cell handover in telecommunication system supporting carrier aggregation

ABSTRACT

A method, device and system for a cell handover in a telecommunication system supporting carrier aggregation. The method may include: a Base Station (BS) determines that whether carrier components corresponding to one or more cells to be accessed are in the same frequency band, wherein the one or more cells to be accessed belong to a target BS, and are selected by a terminal which needs to perform the cell handover and is served by the BS; if yes, the BS encapsulates configuration information of all the cells in the one or more cells to be accessed in a handover command for initiating cell handover; otherwise, the BS encapsulates configuration information of one or more cells in the one or more cells to be accessed in the handover command, and sends the handover command to the target BS.

CROSS REFERENCE TO RELATED APPLICATIONS

The application is based on the PCT Application No. PCT/CN2011/075073filed on Jun. 1, 2011 and entitled “Method, Device and System for CellHandover in Telecommunication System Supporting Carrier Aggregation”,claiming priority to Chinese Application No. 201010240485.3 filed onJul. 27, 2010 and entitled “Method, Device and System for Cell Handoverin Communication System Supporting Carrier Aggregation”. The contents ofboth of the applications are incorporated herein by reference.

FIELD

The invention relates to the field of communications supporting carrieraggregation (CA), and particularly to methods and apparatuses for cellhandover in a communication system supporting carrier aggregation, andterminal devices, base stations and communication systems including suchapparatuses or using such methods.

BACKGROUND

The future LTE-A (Long Term Evolution-Advanced) system supports atransmission bandwidth up to 100 MHz, while in the current LTE standardthe maximum supportable transmission bandwidth is 20 MHz such that aplurality of carriers need to be aggregated for broader bandwidthtransmission. Carrier aggregation is a technique presented by 3GPP tosupport the higher requirement for transmission bandwidth in the futuremobile communication system, in which a plurality of carriers areaggregated for transmission. The introduction of the CA technique bringsabout new chances and challenges for the development of thecommunication techniques.

SUMMARY

A communication system which supports CA, such as LTE-A, can supportvarious CA scenarios, for example, consecutive CA and non-consecutive CAscenarios. This results in the diversity of the scenarios when aterminal device in a communication system is handed over between cells.Due to such diversity, a single handover algorithm cannot be applied toall the scenarios. Some embodiments of the invention provide a scheme ofadaptively selecting the cell handover algorithms based on the CAscenario in which a terminal device is located when the terminal deviceis to be handed over. Particularly, some embodiments of the inventionmethods and apparatuses for cell handover in a communication systemsupporting CA, and terminal devices, base stations and communicationsystems including such apparatuses or using such methods.

The following presents a simplified summary of the disclosure in orderto provide a basic understanding of some aspects of the disclosure. Thissummary is not an exhaustive overview of the disclosure. It is notintended to identify key or critical elements of the disclosure or todelineate the scope of the disclosure. Its sole purpose is to presentsome concepts in a simplified form as a prelude to the more detaileddescription that is discussed later.

According to an aspect of the invention, there is provided a method forcell handover in a communication system supporting carrier aggregation,which may include: selecting, by a terminal device in the communicationsystem when the terminal device moves to edge of a currently servingcell, one or more from one or more neighbor cells based on carrieraggregation manners of the one or more neighbor cells, as objects to bemeasured; measuring, by the terminal device, performances of the objectsto be measured to obtain one or more measurement results; andtransmitting, by the terminal device, the one or more measurementresults to a source base station currently serving the terminal device,as a performance measurement report of the one or more neighbor cells.

According to another aspect of the invention, there is provided anapparatus for cell handover, configured in a terminal device in acommunication system supporting carrier aggregation and including: ameasurement object selecting device, configured to select, when theterminal device moves to edge of a currently serving cell, one or morefrom one or more neighbor cells based on carrier aggregation manners ofthe one or more neighbor cells, as objects to be measured; a cellmeasuring device, configured to measure performances of the objects tobe measured to obtain one or more measurement results; and atransmitting device, configured to transmit the one or more measurementresults obtained by the cell measuring device to a source base stationcurrently serving the terminal device, as a performance measurementreport of the one or more neighbor cells.

According to another aspect of the invention, there is provided aterminal device in a communication system supporting carrieraggregation. The terminal device may include the above apparatus forcell handover.

According to another aspect of the invention, there is provided a methodfor cell handover in a communication system supporting carrieraggregation. The method includes: selecting, by a source base stationwhen receiving a performance measurement report of one or more neighborcells from a terminal device served by the source base station, analgorithm suitable to the carrier aggregation manners of one or morecandidate base stations corresponding to the one or more neighbor cellsbased on the performance measurement report and based on the carrieraggregation manners to calculate priorities of the one or more candidatebase stations; selecting one having highest priority from the one ormore candidate base stations, as a destination base station; andselecting one or more cells to be accessed for the terminal device fromall cells belonging to the destination base station in the one or moreneighbor cells.

According to another aspect of the invention, there is provided anapparatus for cell handover, configured in the base station of thecommunication system supporting carrier aggregation and including: areceiving device configured to receive a performance measurement reportof one or more neighbor cells from a terminal device served by the basestation; a priority determining device configured to select an algorithmsuitable to the carrier aggregation manners of one or more candidatebase stations corresponding to the one or more neighbor cells based onthe performance measurement report and based on the carrier aggregationmanners to calculate priorities of the one or more candidate basestations; a destination base station selecting device configured toselect one having highest priority from the one or more candidate basestations, as a destination base station; and a cell selecting deviceconfigured to select one or more cells to be accessed for the terminaldevice from all cells belonging to the destination base station in theone or more neighbor cells.

According to another aspect of the invention, there is provided a basestation in a communication system supporting carrier aggregation. Thebase station includes the above apparatus for cell handover.

According to another aspect of the invention, there is provided a methodfor cell handover in a communication system supporting carrieraggregation. The method includes: judging, by a source base station inthe communication system, whether or not the component carrierscorresponding to one or more cells to be accessed belonging to adestination base station selected by a terminal device which is servedby the source base station and is to be handed over are in a samefrequency band, and if yes, packaging configuration information of allthe cells to be accessed in a handover command for initiating thehandover of the terminal device, otherwise, packaging configurationinformation of one of the cells to be accessed in the handover command;and transmitting the handover command.

According to another aspect of the invention, there is provided anapparatus for cell handover, configured in a base station in thecommunication system supporting carrier aggregation and including: ademand forming device configured to judge whether or not the componentcarriers corresponding to one or more cells to be accessed belonging toa destination base station selected by a terminal device which is servedby the present base station and is to be handed over are in a samefrequency band, and if yes, package configuration information of all thecells to be accessed in a handover command for initiating the handoverof the terminal device, otherwise, package configuration information ofone of the cells to be accessed in the handover command; and atransmitting device configured to transmit the handover command.

According to another aspect of the invention, there is provided a basestation in a communication system supporting carrier aggregation. Thebase station includes the above apparatus for cell handover.

According to another aspect of the invention, there is provided a methodfor cell handover in a communication system supporting carrieraggregation. The method includes: selecting, by a terminal device in thecommunication system when the terminal device moves to edge of acurrently serving cell, one or more from one or more neighbor cellsbased on carrier aggregation manners of the one or more neighbor cells,as objects to be measured; measuring, by the terminal device,performances of the objects to be measured to obtain one or moremeasurement results; transmitting, by the terminal device, the one ormore measurement results to a source base station currently serving theterminal device, as a performance measurement report of the one or moreneighbor cells; selecting, by the source base station when receiving theperformance measurement report from the terminal device, an algorithmsuitable to the carrier aggregation manners of one or more candidatebase stations corresponding to the one or more neighbor cells based onthe performance measurement report and based on the carrier aggregationmanners to calculate priorities of the one or more candidate basestations; selecting one having highest priority from the one or morecandidate base stations, as a destination base station; and selectingone or more cells to be accessed for the terminal device from all cellsbelonging to the destination base station in the one or more neighborcells.

According to another aspect of the invention, there is provided a methodfor cell handover in a communication system supporting carrieraggregation. The method includes: selecting, by a terminal device in thecommunication system when the terminal device moves to edge of acurrently serving cell, one or more from one or more neighbor cellsbased on carrier aggregation manners of the one or more neighbor cells,as objects to be measured; measuring, by the terminal device,performances of the objects to be measured to obtain one or moremeasurement results; transmitting, by the terminal device, the one ormore measurement results to a source base station currently serving theterminal device, as a performance measurement report of the one or moreneighbor cells; selecting, by the source base station when receiving theperformance measurement report from the terminal device, one from one ormore candidate base stations corresponding to the one or more neighborcells based on the performance measurement report, as a destination basestation, and selecting one or more cells to be accessed for the terminaldevice from all cells belonging to the destination base station in theone or more neighbor cells; if component carriers corresponding to thecells to be accessed are in a same frequency band, packagingconfiguration information of all the cells to be accessed in a handovercommand for initiating cell handover; otherwise, packaging configurationinformation of one or more among the cells to be accessed in thehandover command; and transmitting the handover command.

According to another aspect of the invention, there is provided acommunication system supporting carrier aggregation, including the aboveterminal device and/or the above base station.

In addition, some embodiments of the disclosure further provide computerprogram for realizing the above methods.

Further, some embodiments of the disclosure further provide computerprogram products in at least the form of computer-readable medium, uponwhich computer program codes for realizing the above methods arerecorded.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the embodimentsof the disclosure can be better understood with reference to thedescription given below in conjunction with the accompanying drawings,throughout which identical or like components are denoted by identicalor like reference signs. In addition the components shown in thedrawings are merely to illustrate the principle of the disclosure. Inthe drawings:

FIG. 1 is a schematic flow chart showing a method of cell handover for aterminal device in a communication system according to an embodiment ofthe invention;

FIG. 2 is a schematic flow chart showing a method of a terminal deviceselecting an object to be measured according to an embodiment of theinvention;

FIG. 3 is a schematic flow chart showing a method of filtering themeasure results by a terminal device before sending a performancemeasurement report to a source base station according to an embodimentof the invention;

FIG. 4 is a schematic flow chart showing a method of filtering themeasure results by a terminal device before sending a performancemeasurement report to a source base station according to anotherembodiment of the invention;

FIG. 5 is a schematic flow chart showing an method of object comparisonin order to filter the measure results by a terminal device according toan embodiment of the invention;

FIG. 6 is a schematic flow chart showing an method of object comparisonin order to filter the measure results by a terminal device according toanother embodiment of the invention;

FIG. 7 is a schematic block diagram showing the structure of anapparatus for cell handover according to an embodiment of the invention;

FIG. 8 is a schematic block diagram showing the structure of anapparatus for cell handover according to another embodiment of theinvention;

FIG. 9 is a schematic flow chart showing a method for cell handoverperformed by a source base station in a communication system accordingto an embodiment of the invention;

FIG. 10 is a schematic flow chart showing a method of calculating by asource base station the priority of a candidate base station based onthe performance measurement report sent from the terminal deviceaccording to an embodiment of the invention;

FIG. 11 is a schematic flow chart showing a method of selecting by asource base station a cell to be accessed based on the CA manners of adestination base station according to an embodiment of the invention;

FIG. 12 is a schematic flow chart showing a method of selecting by asource base station a primary cell to be accessed based on the CAmanners of a destination base station according to an embodiment of theinvention;

FIG. 13 is a schematic flow chart showing a method of forming by asource base station a handover command based on the CA manner of theselected cell to be accessed according to an embodiment of theinvention;

FIG. 14 is a schematic block diagram showing the structure of anapparatus for cell handover configured in a base station of acommunication system supporting CA according to an embodiment of theinvention;

FIG. 15 is a schematic flow chart showing a method of cell handoverperformed by a source base station in a communication system accordingto an embodiment of the invention;

FIG. 16 is a schematic block diagram showing the structure of anapparatus for cell handover configured in a base station of acommunication system supporting CA according to an embodiment of theinvention;

FIG. 17, FIG. 18, and FIG. 19 each show an application scenario to whichthe methods of cell handover according to the above embodiments can beapplied;

FIG. 20 is a schematic block diagram showing the structure of anapparatus for cell handover configured in a base station of acommunication system supporting CA according to another embodiment ofthe invention; and

FIG. 21 is a schematic block diagram showing the structure of a computerwith which the embodiments of the invention can be realized.

DETAILED DESCRIPTION

Some embodiments of the present disclosure will be described inconjunction with the accompanying drawings hereinafter. It should benoted that the elements and/or features shown in a drawing or disclosedin an embodiments may be combined with the elements and/or featuresshown in one or more other drawing or embodiments. It should be furthernoted that some details regarding some components and/or processesirrelevant to the disclosure or well known in the art are omitted forthe sake of clarity and conciseness.

Some embodiments of the present disclosure provide a scheme ofadaptively selecting the cell handover algorithms based on the CAscenario in which a terminal device is located when the terminal deviceis to be handed over. In the disclosure, a base station (BS) to which acurrently serving cell of a terminal device belongs is referred to as asource base station (i.e. a base station currently serving the terminaldevice), a base station to which a neighbor cell of the terminal devicebelongs is referred to a candidate destination base station or acandidate base station, and a base station to which a cell, to which theterminal device is finally handed, belongs is referred to as adestination base station. The so-called neighbor cell refers to a cellwhose coverage is adjacent to that of the currently serving cell of aterminal device, which may be detected by the terminal device when theterminal device moves to the edge of the coverage of the currentlyserving cell.

FIG. 1 shows a method of a terminal device being handed over betweencells in a communication system supporting CA according to an embodimentof the invention.

When a terminal device is to perform cell handover, the terminal deviceneeds to measure the performances of its neighbor cells. At this time,the terminal device is located at the edge of the coverage of thecurrently serving cell, and may detect one or more neighbor cells at thesame time. These neighbor cells may belong to different candidate basestations which may support various carrier aggregation manners. With thedifferent carrier aggregation manners, these neighbor cells may presentdifferent characteristics. In the embodiment shown in FIG. 1, theterminal device selects a part or all of the neighbor cells as theobject to be measured, based on the different characteristics of theseneighbor cells under the different carrier aggregation manners.

As shown in FIG. 1, the method may include step 103, step 109 and step115.

In step 103, based on the detected carrier aggregation manners of one ormore neighbor cells, one or more are selected from one or more neighborcells, as the objects to be measured. In other words, the objects to bemeasured are selected by using the different characteristics of theseneighbor cells under different carrier aggregation manners, rather thansimply measuring all the neighbor cells. As an example, the selection ofthe object to be measured may be performed by the source base station ofthe terminal device, and then the result of the selection may benotified to the terminal device by the source base station; as anotherexample, the selection of the object to be measured may be performed bythe terminal device.

In step 109, the terminal device measures the performances of one ormore objects to be measured obtained at step 103, to obtain one or moremeasurement results. In step 115, the terminal device forms theperformance measurement report of one or more neighbor cells by usingthese measurement results, and transmits the performance measurementreport to the source base station.

By using the method shown in FIG. 1, the number of cells to be measuredmay be reduced, thereby reducing the measurement load of the terminaldevice and improving the processing speed.

It shall be noted that the terminal device may measure the performanceof a cell by using any appropriate method and the performance of a cellmay be characterized by any one or more appropriate performanceparameters, as the measurement result of the cell. In the disclosure thedescription of the particular measuring method and performanceparameters is omitted. The measured performance parameters of a cell arecollectively referred to as the performance of the cell.

FIG. 2 shows a method of selecting an object to be measured from one ormore neighbor cells according to another embodiment of the invention. Inconsecutive carrier aggregation scenario, the component carriers (CCs)corresponding to the neighbor cells belonging to a candidate basestation are located in the same frequency band, and thus these componentcarriers have similar propagation characteristics. By using suchcharacteristics, one neighbor cell may be selected from the neighborcells belonging to the candidate base station, as the object to bemeasured. The measurement result of the object may be used as themeasurement result of all the neighbor cells belong to the candidatebase station.

As shown in FIG. 2, in step 103-1, it is determined whether thecomponent carriers corresponding to the neighbor cells belonging to thesame base station among one or more neighbor cells are located in thesame frequency band. That is, it is judged first whether the neighborcells belonging to the same base station are of consecutive carrieraggregation manner. If yes, in step 103-2 one or more (preferably, one)are selected from the neighbor cells belonging to the same base station,as the objects to be measured. If not, in step 103-3 all of the neighborcells belonging to the same base station are determined as the objectsto be measured. Particularly, if only one neighbor cell belongs to acandidate base station, this neighbor cell is determined as the objectto be measured. If a plurality of neighbor cells belongs to a candidatebase station and these neighbor cells are in different frequency bands,all the neighbor cells belonging to the candidate base station aredetermined as the objects to be measured. If a plurality of neighborcells belongs to a candidate base station and these neighbor cells arein the same frequency bands, it is not necessary to use all the neighborcells belonging to the candidate base station as the objects to bemeasured. The steps in FIG. 2 may be performed by a terminal device thatperforms cell hand over or may be performed by the source base stationof the terminal device.

In the embodiment of FIG. 2, the spectrum features and propagationfeatures of the cell in consecutive carrier aggregation manner are takenadvantage of to reduce the number of neighbor cells to be measured,thereby significantly reduce the measurement load of the terminaldevice. In other embodiment or example, the object to be measured may beselected by using other appropriate characteristics of a neighbor cellin other type of carrier aggregation manner, which are not numeratedherein.

It shall be noted that the above method of selecting an object to bemeasured may be applied to other embodiments of the method for cellhandover described above and to be described below.

In some embodiments, before sending the measurement results to thesource base station, the terminal device may further perform a selectionamong these measurement results according to some conditions. Only themeasurement results which meet the conditions will be sent to the sourcebase station. In this way the number of measurement results to beprocessed by the communication system may be reduced, thereby reducingthe transmission load on the communication channel and the processingload of the source base station. FIGS. 3-6 respectively shows someparticular embodiments of the method of optimizing the measurementresults by the terminal device.

In the embodiment of FIG. 3, the terminal device sets a transmissionthreshold for the measurement results, to reduce the number ofmeasurement reports to be processed, thereby reducing the transmissionload on the communication channel and the processing load of the sourcebase station. As shown in FIG. 3, in step 110 the terminal devicedetermines whether each of one or more measurement results is higherthan a threshold, and if yes, the terminal device transmits themeasurement result to the source base station in step 115, particularly,it may include the measurement result in the performance measurementreport to be transmitted to the source base station. If a measurementresult is lower than the threshold, the terminal device does not sendthe measurement result to the source base station, e.g. the measurementresult will not be included in the performance measurement report to besent to the source base station. It shall be noted that the abovethreshold may be set as actual requirements, e.g. may be set based onthe measured performance parameters or the actual communicationscenarios, the description of which is omitted herein. As an example,the above threshold may be a value set for the terminal device by thesystem or base station, or may be a value determined by the terminaldevice based on the actual application scenario. As another example, theabove threshold may be pre-provided in the terminal device.

In the embodiment shown in FIG. 4, the terminal device or its sourcebase station specifies the object to be compared with the measurementresults based on the carrier aggregation manner of the source basestation, so that the method of selecting the measurement results may beadapted to the actual communication scenario. In addition thetransmission of the measurement report may be optimized. Particularly,when the source base station is of consecutive carrier aggregationmanner, due to the similar propagation characteristics of the componentcarriers in the same frequency band, any one of the cells of the sourcebase station may be used as the object to be compared and may bemeasured, thereby reducing the measurement and processing load of theterminal device and improving the processing speed. In the case that thesource base station is of non-consecutive carrier aggregation manner,the propagation characteristics of the cells are different from eachother since the component carriers of the cells are located in differentfrequency bands. In this case, all the cells of the source base stationmay be used as the objects to be compared and may be measured. As shownin FIG. 4, in step 111 the terminal device or the source base stationdetermines whether the component carriers corresponding to all the cellsof the source base station (or all the cells to which the terminaldevice is connected) are located in different frequency bands.

If the determining result of step 111 is YES, in step 112 the terminaldevice compares each measurement result with the performances of all thecells of the source base station, or compares each measurement resultwith a threshold value (Similar to the embodiment shown in FIG. 3, thethreshold value may be predetermined by the system, or the base stationor the terminal device, or may be determined based on actual applicationscenario by the system, or the base station or the terminal device, thedescription of which is omitted herein). If a measurement result isbetter than the performances of all the cells of the source base stationor is higher than the threshold value, in step 115 the terminal devicemay send the measurement result to the source base station, otherwise,the terminal device does not send the measurement result to the sourcebase station.

If the determining result of step 111 is NO, i.e. if the componentcarriers corresponding to al the cells of the source base station arelocated in the same frequency band, in step 112 the terminal devicecompares each measurement result with the performance of any of all thecells of the source base station, or may compare each measurement resultwith a threshold value ((Similar to the embodiment shown in FIG. 3, thethreshold value may be predetermined by the system, or the base stationor the terminal device, or may be determined based on actual applicationscenario by the system, or the base station or the terminal device, thedescription of which is omitted herein). If a measurement result isbetter than the performance of any cell randomly selected from all thecells of the source base station or is higher than the threshold value,in step 115 the terminal device may send the measurement result to thesource base station, otherwise, the terminal device does not send themeasurement result to the source base station.

As an example, the terminal device may compare a measurement result withthe performances of the cells of the source base station by using thefollowing method shown in FIG. 5 or FIG. 6.

As shown in FIG. 5, the method of comparing a measurement result of aneighbor cell with the performances of all the cells of the source basestation (step 112 as shown in FIG. 4) may include steps 112-1 and 112-2.In step 112-1, one cell which has the best performance among all thecells of the source base station (all the cells of the source basestation to which the terminal device is connected) is used as the objectto be compared. The terminal device measures the performance of theobject to be compared. In step 112-2, the terminal device compares eachmeasurement result with the performance of the cell having the bestperformance. By using the method of FIG. 5, the terminal device needsnot to compare the measurement results with the performances of all thecells of the source base station. In this way, the processing load ofthe terminal device is reduced and processing speed is improved. As anexample, the cell having the best performance among all the cells towhich the terminal device is currently connected may be specified by thesource base station, e.g. based on the performance data stored in thebase station, and may be notified to the terminal device by the sourcebase station. As another example, the terminal device may select thecell having the best performance from all the cells to which it isconnected based on the performance data stored by the terminal device orbased on the history measurement result stored by it, or alternatively,the terminal device may measure all the cells to which it is currentlyconnected, and select one having the best performance there from as theobject to be compared.

As shown in FIG. 6, the method of comparing a measurement result of aneighbor cell with the performance of any one cell of the source basestation (i.e. step 113 shown in FIG. 4) may include steps 113-1 and113-2. In step 113-1, one cell is randomly selected from all the cellsof the source base station (all the cells to which the terminal deviceis currently connected) as an object to be compared. The performance ofthe object may be measured. In step 113-2, the terminal device compareseach measurement result with the performance of the randomly selectedcell. By using the method of FIG. 6, the terminal device needs tomeasure only the performance of one cell of the source base station. Inthis way the measurement and processing load of the terminal device canbe reduced and the processing speed can be improved. As an example, thesource base station may randomly specify one of all the cells, to whichthe terminal device is currently connected, as the object to becompared, and notify the specified object to the terminal device. Asanother example, the terminal device may randomly select one cell fromall the cells, to which the terminal device is currently connected, asthe object to be compared.

It shall be noted that the methods of processing the measurement resultsin the embodiments/examples in FIGS. 3-6 may be applied to otherembodiments of the method for cell handover of the disclosure.

FIG. 7 and FIG. 8 each show an apparatus which realizes the method shownin the above embodiments/example. The apparatus 700 or 800 shown in FIG.7 or FIG. 8 may be configured in a terminal device (not shown) of acommunication system supporting carrier aggregation.

As shown in FIG. 7, the apparatus for cell handover 700 includes ameasurement object selecting device 701, a cell measuring device 702 anda transmitting device 703.

When the terminal device moves to the edge of the coverage of thecurrently serving cell, the measurement object selecting device 701 isconfigured to select one or more from one or more detected neighborcells based on the carrier aggregation manners of the one or moredetected neighbor cells, as the objects to be measured.

The cell measuring device 702 is configured to measure the performancesof the one or more selected objects to be measured, to obtain one ormore measurement results. The transmitting device 703 is configured toform a performance measurement report of the one or more neighbor cellsbased on measurement results obtained by the cell measuring device 702,and transmit the performance measurement report to the source basestation currently serving the terminal device.

Similar to the method embodiment of FIG. 1, the apparatus 700 selectsthe objects to be measured by using the different characteristics of thedetected neighbor cells, in stead of simply measuring all the neighborcells. In this way, the number of cells to be measured may be reduced,thereby reducing the measurement load of the terminal device andimproving the processing speed.

As shown in FIG. 8, the apparatus 800 for cell handover includes ameasurement object selecting device 801, a cell measuring device 802 anda transmitting device 803. The difference from that shown in FIG. 7 liesin that, the apparatus 800 for cell handover further includes a judgingdevice 804.

The measurement object selecting device 801, the cell measuring device802 and the transmitting device 803 are respectively similar to thosedevices 701, 702, and 703 in FIG. 7, the description of which is notrepeated. The judging device 804 is configured to judge whether eachmeasurement result obtained by the cell measuring device 801 is higherthan a threshold value, and if yes, instruct the transmitting device 803to transmit the measurement result to the source base station,otherwise, do not instruct the transmitting device 803 to transmit themeasurement result to the source base station.

In the embodiment of FIG. 8, the apparatus 800 sets a transmissionthreshold for the measurement results, in order to reduce the number ofmeasurement reports to be processed, thereby reducing the transmissionload on the transmission channel and the processing load of the sourcebase station.

In another embodiment, the judging device 804 may further select theobject to be compared with the measurement results according to thecarrier aggregation manner of the source base station. Particularly, thejudging device 804 may firstly determine whether the component carrierscorresponding to all the cells of the source base station are located indifferent frequency bands. If the component carriers corresponding toall the cells of the source base station are located in differentfrequency bands, the judging device 804 further judges whether eachmeasurement result obtained by the cell measuring device 802 is betterthan the performances of all the cells of the source base station or ishigher than a threshold value, and if yes, instructs the transmittingdevice 803 to transmit the measurement result to the source basestation, otherwise, does not instruct to transmit the measurement resultto the source base station. If it is determined that the componentcarriers corresponding to all the cells of the source base station arelocated in the same frequency band, the judging device further judgeswhether each measurement result obtained by the cell measuring device802 is better than the performance of a cell randomly selected from allthe cells of the source base station or is higher than a thresholdvalue, and if yes, instructs the transmitting device 803 to transmit themeasurement result to the source base station, otherwise, does notinstruct to transmit the measurement result to the source base station.In this way, the selection of the measurement results may be adapted tothe actual communication scenario, thereby further optimizing thetransmission of the measurement report. In the case of consecutivecarrier aggregation manner, any one cell is selected randomly form thecells of the source base station as the object t be compared and ismeasured, which may reduce the measurement and processing load of theterminal device and improve the processing speed.

As an example, the apparatus 800 may compare a measurement result withthe performances of the cells of the source base station by using theabove method shown in FIG. 5 or FIG. 6. For example, the cell measuringdevice 802 may measure the performances of all the cells of the sourcebase station and return the results to the judging device 804. Thejudging device 804 may select one cell having the best performance fromall the cells of the source base station based on the performances ofall the cells measured by the cell measuring device, and compare eachmeasurement result with the performance of the cell having the bestperformance. In this way, the apparatus 800 needs not to compare themeasurement results with the performances of all the cells of the sourcebase station. Thus the processing load of the apparatus can be reducedand the processing speed can be accelerated. For another example, thecell measuring device 802 may measure the performance of a cell randomlyselected from all the cells of the source base station; and the judgingdevice 804 may compare the measurement results of the neighbor cellswith the performance of the randomly selected cell. In this way, theapparatus 800 needs only to measure the performance of one cell of thesource base station. Thus, the measurement and processing load can bereduced and the processing speed can be accelerated.

Similar to the above method embodiments and examples, in the aboveapparatus embodiments and examples the threshold value may be set by thesystem (or base station) or by the terminal device as practicalrequirements, the description of which is not repeated.

Similar to the above method embodiments, the apparatus 700 or 800 maymeasure the performance of a cell by using any appropriate method andthe performance of the cell may be characterized by any appropriateperformance parameters, the description of which is omitted herein.

As an example, the measurement object selecting device 701 or 801 mayfurther judge the component carriers corresponding to the neighbor cellsbelonging to the same base station among the one or more detectedneighbor cells are located in different frequency bands; and if yes,select one neighbor cell randomly as the object to be measured,otherwise, use all the neighbor cells belonging to the same base stationas the object to be measured. In this example, the spectrumcharacteristic and propagation characteristic of the cells of theconsecutive carrier aggregation manner are taken into account, to reducethe number of neighbor cells to be measured, and thus reduce themeasurement load of the terminal device. In other embodiment or example,the measurement object selecting device 701 or 801 may select theobjects to be measured by using other appropriate characteristics of theneighbor cells in other types of CA scenarios, which are not numeratedherein

Some embodiments of the invention further provide terminal devices inthe communication system supporting carrier aggregation. The terminaldevice may include the apparatus for cell handover in the aboveembodiments or examples, or may use the method of cell handover in theabove embodiments or examples, the description of which is not repeated.

In addition, in the embodiments described above with reference to FIGS.7-8, the object to be measured is selected at the side of the terminaldevice. Selecting the object to be measured by the terminal device (instead of the source base station) can reduce the communication overheadbetween the base station and the terminal device, and thus theprocessing speed and efficiency can be improved. According to anotherembodiment, there is provided a base station (not shown) including theabove apparatus for cell handover, the apparatus for cell handover ofthe base station may include a measurement object determining devicewhich is configured to select one or more from one or more neighborcells detected by a terminal device served by the base station based onthe carrier aggregation manners of the one or more neighbor cells, asthe objects to be measured. Accordingly, the embodiment further providesa method of cell handover at the side of the base station. The methodmay include: selecting one or more from one or more neighbor cellsdetected by a terminal device served by the base station based on thecarrier aggregation manners of the one or more neighbor cells, as theobjects to be measured; and notifying the objects to be measured to theterminal device. Particularly, the base station (for example, by usingthe measurement object determining device) firstly determines whetherthe component carriers corresponding to the neighbor cells belonging tothe same base station among the one or more neighbor cells are locatedin the same frequency band; if yes, selects one or more (preferably,one) from the neighbor cells belonging to the same base station as theobjects to be measured, if not, uses all the neighbor cells belonging tothe same base station as the objects to be measured. Then thetransmitting device of the base station notifies the objects to bemeasured to the terminal device. As an example, the measurement objectdetermining device may be incorporated in the apparatus for cellhandover at the base station side according to the embodiments orexamples to be described blow. In addition, the method of selecting anobject to be measured by a base station may be incorporated in themethod for cell handover performed at the base station side according tothe embodiments or examples to be described blow.

The methods and apparatuses of selecting a destination base station anda cell to be accessed at the base station side in the communicationsystem supporting carrier aggregation, as well as a base station and acommunication system including such an apparatus.

In conventional single carrier communication system, a terminal deviceis connected to only one cell at the same time. When performing cellhandover, a unique cell to be accessed can be determined based only onthe measurement report of the neighbor cells, i.e. the uniquedestination base station can be determined. In the CA supportingscenarios, before performing cell handover, the terminal device may beconnected to a plurality of cells at the same time and these cellscorrespond to a same source base station. After the cell handover isperformed, the terminal device may be still connected to a plurality ofcells at the same time. If the cells to be accessed are selected basedon only the performances of the neighbor cells, there is a possibilitythat the selected cells may belong to different base stations. Someembodiments of the invention provide a policy or scheme of selecting thedestination base station and the cells to be accessed by the source basestation in the CA supporting scenario.

FIG. 9 shows an embodiment which illustrates a method of selecting adestination base station and cells to be accessed by a base station(referred to as the source base station) in the communication systemsupporting carrier aggregation according to the performance measurementreport of the neighbor cells of a terminal device served by the basestation transmitted by the terminal device.

As shown in FIG. 9, the method includes steps 903, 908 and 915. In step903, the source base station receives the performance measurement reportof the neighbor cells of a terminal device served by the base stationtransmitted by the terminal device. The performance measurement reportmay include the measurement results of one or more neighbor cellsobtained by the terminal device. These neighbor cells may correspond toone or more candidate base stations. The source base station may selectdifferent algorithms based on the different carrier aggregation mannersof the different candidate base stations, to calculate the priorities ofthese candidate base stations. Then in step 909, the source base stationselect one having the highest priority from these candidate basestations based on the calculated priorities, as the destination basestation. In step 915, the source base station selects one or more fromall the cells belonging to the destination base station in the one ormore neighbor cells, as the cells to be accessed of the terminal device.

Since the candidate base stations may support different carrieraggregation manners, the neighbor cells thereof may present differentcharacteristics. In the embodiment shown in FIG. 9, the source basestation adaptively selects the algorithm of calculating the prioritiesbased on the carrier aggregation manners of these neighbor cells. Inthis way the selection of the destination base station may be moreadapted to the actual communication scenario. In addition, in the methodthe destination base station is determined first and the cells to beaccessed are then selected from the cells of the destination basestation. In this way, the case that the selected cells to be accessedbelong to different base stations can be avoided.

FIG. 10 shows a particular embodiment of selecting different prioritycalculating algorithms according to the carrier aggregation scenarios ofthe candidate base stations.

As shown in FIG. 10, the method of selecting different prioritycalculating algorithms according to the carrier aggregation scenarios(e.g. step 903) may include steps 903-1, 903-2 and 903-3. In step 903-1,the source base station firstly judges whether the component carrierscorresponding to the neighbor cells belonging to the same candidate basestation among the one or more neighbor cells related to the performancemeasurement report are located in the same frequency bands. As describedabove, these neighbor cells may correspond to one or more candidate basestations.

If more than one neighbor cell corresponds to the same candidate basestation and these neighbor cells are provided in the same frequencyband, in step 903-2 the source base station calculates the priority ofthe candidate base station based on the performances of all the neighborcells belonging to the candidate base station (If only one neighbor cellcorresponds to a candidate base station, the priority of the candidatebase station may be determined based on the performance of this neighborcell). As an example, the source base station may calculate the sum ofthe performances of all the neighbor cells belonging to the candidatebase station based on the measurement results in the performancemeasurement report, or may weight the performances of all the neighborcells belonging to the candidate base station and then calculate the sumof the weighted performances. Then the source base station may determinethe priority of the candidate base station based on the value of thecalculated sum. The larger the sum is, the higher the priority is. Itshall be noted that the weights may be determined according to thefunctions of the neighbor cells and the actual application scenario, thedescription of which is not detailed herein.

If more than one neighbor cell corresponds to the same candidate basestation and these neighbor cells are provided in different frequencybands, in step 903-3 the source base station determines the priority ofthe candidate base station based on the performance of one neighbor cellhaving the best performance among all the neighbor cells belonging tothe candidate base station in the performance measurement report. Thehigher the performance of the neighbor cell having the best performanceis, the higher the priority of the candidate base station is.

In the embodiment of FIG. 10, different methods of calculatingpriorities are selected based on whether or not the consecutive CAscenario or non-consecutive CA scenario is involved, to obtain thepriorities of the candidate base stations.

In CA supporting scenario, the selected destination base station maysupport CA. Thus, the terminal device, after being handed over to thedestination base station, may be connected to a plurality of cells. Asan example, all the cells of the destination base station may beselected as the cells to be accessed for the terminal device. As anotherexample, all the neighbor cells belonging to the destination basestation in the one or more neighbor cells may be selected as the cellsto be accessed for the terminal device, or one or more may be selectedfrom all the neighbor cells belonging to the destination base station inthe one or more neighbor cells, as the cells to be accessed for theterminal device. FIGS. 11-12 each shows another particular example ofselecting the cells to be accessed by using different manners based onthe different CA supporting scenarios.

As shown in FIG. 11, the method of selecting the cells to be accessedfrom the cells of the destination base station (e.g. step 915) mayinclude steps 915-1, 915-2 and 915-3. In step 915-1 the source basestation determines whether or not the component carriers correspondingto all the cells belonging to the destination base station among one ormore neighbor cells involved in the performance measurement report areprovided in the same frequency band, that is, determines whether thecarrier aggregation manner of the destination base station isnon-consecutive or not.

If determining that the component carriers corresponding to all theneighbor cells belonging to the destination base station are provided inthe same frequency band, in step 915-2 the source base station selectsone or more neighbor cells from all the neighbor cells belonging to thedestination base station, as the cells to be accessed. If only oneneighbor cell belongs to the destination base station, this neighborcell is determined as the cell to be accessed.

If determining that the component carriers corresponding to all theneighbor cells belonging to the destination base station are provided indifferent frequency bands, in step 915-3 the source base station selectsone or more neighbor cells from all the neighbor cells belonging to thedestination base station, as the cells to be accessed. For example, thesource base station the source base station may select one or moreneighbor cells provided in the same frequency band from all the neighborcells belonging to the destination base station, as the cells to beaccessed; or, the source base station may select one or more neighborcells provided in different frequency bands based on the practicalrequirements, as the cells to be accessed.

As an example, after selecting one or more cells to be accessed, e.g.after the step 915, the source base station may select one from theselected cells to be accessed as the primary cell to be accessed, asshown by the dotted line block 916 in FIG. 11. The primary cell to beaccessed refers to the first cell to which the terminal device isconnected to in the case that there is a plurality of cells to beaccessed when performing cell handover. The terminal device may beconnected to the primary cell firstly. After being connected to theprimary cell, the terminal device may be connected to the other cells tobe accessed by adding or actuating component carriers. For example, thecomponent carriers corresponding to other cells to be accessed may beadded by using RRC connection reconfiguration manner excluding mobilecontrol message, so as to realize the CA transmission mode with arelatively small overhead.

FIG. 12 shows an example of selecting the primary cell to be accessedbased on the CA scenarios. As shown in FIG. 12, the method of selectingone primary cell to be accessed from a plurality of cells to be accessed(e.g. step 916) includes steps 916-1, 916-2 and 916-3. In step 916-1,the source base station judges, among the selected one or more cells tobe accessed determined by using the performance measurement report,whether there is a cell whose component carriers are in the samefrequency band as the component carriers corresponding to the currentlyserving cell of the terminal device. If there is such a cell, in step916-2 the cell is selected as the primary cell to be accessed. If thereis not such a cell, in step 916-3 one having the best performance may beselected from all the cells to be accessed based on the performancemeasurement report, as the primary cell to be accessed.

In the example shown in FIG. 12, the cell whose frequency is the samewith that of the currently serving cell of the terminal device isselected as the primary cell to be accessed as far as possible. In thisway, the handover overhead resulted from the inconsistency betweenfrequencies of the cell before handover and the cell after the handovermay be reduced, thereby further reducing the interrupt time of thecommunication.

As an example, the other cells to be accessed may be connected to theterminal device by adding a carrier using RRC (Radio Source Control)connection reconfigure manner excluding mobile control information. Inthis way, the CA transmission may be realized with a relatively smalloverhead. It shall be noted that there are two types of RRC connectionreconfigure manners. The first type is a reconfigure containing mobilecontrol information, i.e. handover. The second type is a reconfigureexcluding mobile control information. In the handover manner (i.e. thefirst type), MAC (Media Access Control) layer, PDCP (Packet DataConvergence Protocol) layer, and RLC (Radio Link Control) layer all needto be reconfigured, and the security key needs also to be reconfigured.This results in a large overhead. In contrast, the second type needs notto reconfigure the above functions, and thus brings about a relativelysmall overhead.

In another example, the source base station may select one having thebest performance from all the neighbor cells belonging to thedestination base station (or from the cells to be accessed selected bythe source base station) based on the performance measurement report, asthe primary cell to be accessed.

FIG. 13 shows another method for cell handover according to anotherembodiment of the invention. As shown in FIG. 13, after determining thedestination base station and the cells to be accessed (It shall be notedthat the destination base station and the cells to be accessed can bedetermined by using the method in the above embodiments or examples),the process of the source base station forming a handover command andtransmitting the handover command may include steps 917, 919, 921 and923.

In step 917, the source base station judges whether the componentcarriers corresponding to the one or more selected cells to be accessedare provided in the same frequency band. If yes, in step 919 the sourcebase station packages the configuration information of all the cells tobe accessed in a handover command indicating initiation of cell handoverof the terminal device. Otherwise, in step 921 the source base stationpackages the configuration information of only the primary cell to beaccessed in the handover command. Finally in step 923, the source basestation transmits the handover command to the destination base station.

In the method of FIG. 13, if the number of the selected cells to beaccessed is larger than 1 and the component carriers corresponding tothese cells to be accessed are provided in the same frequency band, thesource base station packages the information of all the cells to beaccessed in the handover command. Thus, the terminal device can beconnected to all the cells to be accessed at a time. That is, afterbeing handed over, the terminal device can enter the CA mode directly.If the terminal device uses CA communication mode before being handedover, the quality of service for the user can be ensured since thedifferences between the qualities of service before and after thehandover can be reduced. If the number of selected cells to be accessedis larger than 1 and the component carriers corresponding to these cellsto be accessed are provided in different frequency bands, the terminaldevice can firstly be connected to the primary cell. After beingconnected to the primary cell, the terminal device may be connected tothe other cells to be accessed by adding component carriers, forexample, the component carriers corresponding to the other cells to beaccessed can be added by using RRC connection reconfigure mannerexcluding mobile control information, thereby the CA transmission modecan be realized with a relatively small overhead. If the selectedprimary cell to be accessed corresponds to component carriers that arein the same frequency band as those in the serving cell of the terminaldevice before the handover, the overhead due to the inconsistencybetween frequencies before and after the handover can be furtherreduced, thereby the interrupt time of the communication can be furthershortened.

As an example, if the terminal device is currently connected to aplurality of cells of the source base station, the terminal device maybe kept in communication with one of the plurality of cells to which itis currently connected to before the handover is completed. Inconventional single carrier communication system (such as LTE system), ahard handover method is generally employed for cell handover. That is,during the handover the terminal device will disconnect itscommunication with the old cell first before being connected to the newcell, which inevitably results in communication interruption; therebythe quality of service for the user may be decreased. In the example,the disadvantages of CA communication are used, that is, the terminaldevice may keep in communication with one or more old cells before beingconnected to the new cell. The communication with the old cells isdisconnected after the terminal device is completely connected to thenew cell. This can significantly reduce the interruption time ofcommunication, and can improve the quality of service experienced by theuser.

FIG. 15 shows a method for cell handover in a communication systemsupporting carrier aggregation according to another embodiment of theinvention. The method is performed by the source base station in thecommunication system.

As shown in FIG. 15, the method may include steps 1517, 1519, 1521 and1523. In step 1517, after selecting a destination base station and oneor more cells to be accessed for a terminal device which is served bythe source base station and is to be handed over, the source basestation determines whether the component carriers corresponding to theselected cells to be accessed are provided in the same frequency band.If yes, in step 1519 the source base station packages the configurationinformation of all the cells to be accessed in a handover commandindicating to initiate the handover for the terminal device. Otherwise,in step 1521 the source base station packages the configurationinformation of only part (one or several cells) of the cells to beaccessed in the handover command. Finally in step 1523, the handovercommand is transmitted. By using this method, in the case that the cellsto be accessed are of consecutive CA mode, the terminal device can beconnected to all the cells to be accessed at a time, that is, theterminal device can enter CA mode directly after the handover. In thecase that the terminal device is in CA communication mode before thehandover, the quality of service for the user can be ensured since thedifferences in qualities of service before and after the handover can bereduced.

FIG. 20 shows a method for cell handover in a communication systemsupporting carrier aggregation according to another embodiment of theinvention. The method is similar to that in FIG. 15; the difference liesin that the method of FIG. 20 may further include a step 2016 ofselecting a primary cell to be accessed. As shown in FIG. 20, the methodmay include steps 2016, 2017, 2019, 2021 and 2023. Steps 2017, 2019,2021 and 2023 are respectively similar to steps 1517, 1519, 1521 and1523 shown in FIG. 15, the description of which is omitted herein. Instep 2016, the source base station may select one from the one or moreselected cells to be accessed, as the primary cell to be accessed. Inthe example, the source base station may package the configurationinformation of only the primary cell to be accessed in the handovercommand in step 2021. It shall be noted that the primary cell to beaccessed can be selected by using the method shown in the aboveembodiments or examples, the description of which is not repeated.

As an example, the method shown in FIG. 15 or 20 may further includesteps of selecting by the source base station the destination basestation and the cells to be accessed, such as steps 2009 and 2015 shownin FIG. 20. For example, in steps 2009 and 2015, the source base stationselects a destination base station from the candidate base stationscorresponding to the neighbor cells of the terminal device and thenselects one or more cells to be accessed from the cells of thedestination base station, based on the performance measurement reporttransmitted from the terminal device. It shall be noted that the sourcebase station may select the destination base station and the cells to beaccessed by using any appropriate method, such as the method in theembodiments or examples described above with reference to FIGS. 9-13,the description of which is not repeated.

FIG. 14 and FIG. 16 each show an embodiment or example of an apparatusfor cell handover in the CA supporting scenario. The apparatus shown inFIG. 14 or 16 is configured in the base station of the communicationsystem supporting carrier aggregation. The devices represented by dottedline blocks in the Figures are optional.

In the embodiment of FIG. 14, the apparatus for cell handover 1400 mayinclude a receiving device 1401, a priority determining device 1402, adestination base station selecting device 1403 and a cell selectingdevice 1404. The receiving device 1400 is configured to receive theperformance measurement report of one or more neighbor cells transmittedfrom a terminal device served by the base station. The prioritydetermining device 1402 is configure to select different algorithms forcalculating the priorities of the candidate base stations based on theperformance measurement report and based on the carrier aggregationmanners of one or more candidate base stations corresponding to the oneor, more neighbor cells. The destination base station selecting device1403 may select one corresponding to the highest priority among thecandidate base stations based on the priorities thereof calculated bythe priority determining device 1402, as the destination base station.The cell selecting device 1404 selects one or more cells to be accessedfor the terminal device from the cells belonging to the destination basestation.

Since the candidate base stations may support different carrieraggregation manners, the neighbor cells thereof may present differentcharacteristics. In the above example, the apparatus in the source basestation adaptively selects different algorithms for calculating thepriorities based on the carrier aggregation manners of these neighborcells. In this way, the selection of the destination base station can bemore adapted to the actual communication scenario. In addition, theapparatus determines the destination base station first, and thenselects the cells to be accessed from the cells of the destination basestation, which avoids the case that the selected cells to be accessedbelong to different base stations.

As a particular example of the embodiment, the priority determiningdevice 1402 may firstly judge whether the candidate base station is ofconsecutive CA mode or non-consecutive CA mode and select an algorithmadapted to the consecutive or non-consecutive CA mode. Particularly, thepriority determining device 1402 may judge whether the componentcarriers corresponding to the neighbor cells belonging to the samecandidate base station among the one or more neighbor cells are providedin the same frequency band.

If more than one neighbor cell corresponds to the same candidate basestation and these neighbor cells are provided in the same frequencyband, the priority determining device 1402 may calculate the priority ofthe candidate base station according to the performances of all theneighbor cells belonging to the candidate base station (if only oneneighbor cell corresponds to a candidate base station, the priority ofthe candidate base station may be determined base on the performance ofthe neighbor cell). As an example, the sum of the performances of theentire neighbor cells belonging to the candidate base station may becalculated based on the measurement results in the performancemeasurement report, or the performances of all the neighbor cellsbelonging to the candidate base station may be weighted and then the sumof the weighted performances may be calculated. Then the priority of thecandidate base station may be determined based on the value of thecalculated sum. The larger the sum is, the higher the priority is. Itshall be noted that the weights may be determined according to thefunctions of the neighbor cells and the actual application scenario, thedescription of which is not repeated.

If more than one neighbor cell corresponds to the same candidate basestation and these neighbor cells are provided in different frequencybands, the priority determining device 1402 may determine the priorityof the candidate base station based on the performance of one neighborcell having the best performance among all the neighbor cells belongingto the candidate base station in the performance measurement report. Thehigher the performance of the neighbor cell having the best performanceis, the higher the priority of the candidate base station is.

As a particular example, the cell selecting device 1404 may furtherselect one or more from all the neighbor cells belonging to thedestination base station among the one or more neighbor cells involvedin the performance measurement report, as the cells to be accessed. Forexample, the cell selecting device 1404 may use all the neighbor cellsbelonging to the destination base station among the one or more neighborcells involved in the performance measurement report, as the cells to beaccessed. As another example, the cell selecting device 1404 may selectone or more from all the cells belonging to the destination basestation, as the cells to be accessed. As examples, the cell selectingdevice 1404 may select the cells to be accessed by using differentmanners based on the different CA supporting scenarios, with the methoddescribed above with reference to FIGS. 11-12, which makes the selectedcells to be accessed more suitable to the actual CA supporting scenario.

For example, the cell selecting device 1404 may firstly determinewhether the component carriers corresponding to all the neighbor cellsbelonging to the destination base station among one or more neighborcells involved in the performance measurement report are in the samefrequency band. If yes, the cell selecting device 1404 may select allthe neighbor cells belonging to the destination base station as thecells to be accessed; otherwise, select one or more from the neighborcells belonging to the destination base station, as the cells to beaccessed. If only one neighbor cell belongs to the destination basestation, the neighbor cell is used as the cell to be accessed.

As an example, the cell selecting device 1404 may further select onefrom the selected cells to be accessed as the primary cell to beaccessed. For example, the cell selecting device 1404 may judge, amongthe selected one or more cells to be accessed, whether there is a cellwhose component carriers are in the same frequency band as the componentcarriers corresponding to the currently serving cell of the terminaldevice; and if there is such a cell, select the cell as the primary cellto be accessed, otherwise, select one having the best performance fromall the neighbor cells belonging to the destination base station basedon the performance measurement report, as the primary cell to beaccessed. For another example, after the destination base stationselecting device 1403 selects the destination base station, the cellselecting device 1404 may further select one having the best performancefrom all the neighbor cells belonging to the destination base station,as the primary cell to be accessed. The cell selecting device 1404 mayselect the primary cell to be accessed by using the above method in theabove embodiments or examples, the description of which is not repeated.

In another example, the apparatus 1400 may further include a demandforming device 1405 and a transmitting device 1406. The demand formingdevice 1405 may form the handover command by using the method shown inFIG. 13. Particularly, the demand forming device 1405 may determinewhether the component carriers corresponding to the selected cells to beaccessed are provided in the same frequency band, if yes, package theconfiguration information of all the cells to be accessed in thehandover command; otherwise, package the configuration information ofonly the primary cell to be accessed in the handover command. Thetransmitting device 1406 is configured to transmit the handover commandto the destination base station. In the example, if the number of theselected cells to be accessed is larger than 1 and the componentcarriers corresponding to these cells to be accessed are provided in thesame frequency band, the terminal device can be connected to all thecells to be accessed at a time. That is, after being handed over, theterminal device can enter the CA mode directly. If the terminal deviceuses CA communication mode before being handed over, the quality ofservice for the user can be ensured since the differences between thequalities of service before and after the handover can be reduced. Inaddition, if the number of selected cells to be accessed is larger than1 and the component carriers corresponding to these cells to be accessedare provided in different frequency bands, the terminal device canfirstly be connected to the primary cell. After being connected to theprimary cell, the terminal device may be connected to the other cells tobe accessed by adding component carriers, for example, the componentcarriers corresponding to the other cells to be accessed can be added byusing RRC connection reconfigure manner excluding mobile controlinformation, thereby the CA transmission mode can be realized with arelatively small overhead.

As an example, if the terminal device to be handed over is currentlyconnected to a plurality of cells of the source base station, theterminal device may be kept in communication with one of the pluralityof cells to which it is currently connected to before the handover iscompleted. For example, the source base station (e.g. the transmittingdevice 1406) may send a command to the terminal device to instruct theterminal device to keep in communication with an old cell. Similar tothe above embodiments or examples, this can significantly reduce theinterruption time of communication, and can improve the quality ofservice experienced by the user.

In the embodiment of FIG. 16, the apparatus 1600 may perform the methodof FIG. 15. Particularly, the apparatus 1600 may include a demandforming device 1605 and a transmitting device 1606.

The demand forming device 1605 is configured to determine whether thecomponent carriers corresponding to the selected cells to be accessedbelonging to the destination base station selected by the present basestation for the terminal device served by the present base station andto be handed over are provided in the same frequency band. If yes, thedemand forming device 1605 packages the configuration information of allthe cells to be accessed in a handover command indicating to initiatethe handover for the terminal device. Otherwise, the demand formingdevice 1605 packages the configuration information of only part (one orseveral cells) of the cells to be accessed in the handover command. Thetransmitting device 1606 transmits the handover command to thedestination base station. By using this apparatus, in the case that thecells to be accessed are of consecutive CA mode, the terminal device canbe connected to all the cells to be accessed at a time, that is, theterminal device can enter CA mode directly after the handover. In thecase that the terminal device is in CA communication mode before thehandover, the quality of service for the user can be ensured since thedifferences in qualities of service before and after the handover can bereduced.

As an example, the apparatus 1600 for cell handover may include aprimary cell selecting device 1607, configured to select one from one ormore selected cells to be accessed, as the primary cell to be accessed.Thus, the demand forming device may package only the configurationinformation of the primary cell in the handover command. In such a case,the terminal device may firstly be connected to the primary cell. Afterthat, the terminal device may be connected to the other cells to beaccessed by adding or actuating component carriers. For example, thecomponent carriers corresponding to the other cells to be accessed maybe added by RRC connection reconfigure mode excluding the mobile controlinformation, thereby the CA transmission mode can be realized with arelative small overhead.

Particularly, the primary cell selecting device 1607 may select onehaving the best performance among the selected cells to be accessedbased on the performance measurement report, as the primary cell to beaccessed.

Alternatively, the primary cell selecting device 1607 may select theprimary cell to be accessed, based on the carriers of the selected cellsto be accessed. Particularly, the primary cell selecting device 1607 mayjudge whether there is a cell, among the selected cells to be accessed,whose corresponding component carriers are in the same frequency band asthe component carriers corresponding to the currently serving cell ofthe terminal device, if yes, select this cell as the primary cell to beaccessed, otherwise, select one having the best performance among allthe neighbor cells belong to the destination base station, as theprimary cell to be accessed. IF the primary cell to be accessed isprovided in the same frequency band as the currently serving cell of theterminal device, the handover overhead due to the inconsistency betweenthe frequencies before and after the handover can be reduced, therebythe interrupt time of communication can be further reduced.

As an example, the apparatus 1600 for cell handover may further includea receiving device 1601, a destination base station selecting device1603 and a cell selecting device 1604. Similar to the above embodimentsor examples, the receiving device 1601 is configured to receive theperformance measurement report of one or more neighbor cells transmittedfrom the terminal device served by the base station. The destinationbase station selecting device 1603 is configure to select one from oneor more candidate base stations corresponding to the one or moreneighbor cells, based on the performance measurement report, as thedestination base station. The destination base station selecting device1603 may select the destination base station by using the method shownin the above embodiments or examples or any other appropriate method.For example, the destination base station selecting device 1603 may besimilar to the device 1403 in FIG. 14, the description of which is notrepeated. The cell selecting device 1604 is configured to select one ormore cells to be accessed for the terminal device from all the neighborcells belonging to the destination base station.

As a particular example, the cell selecting device 1604 may select thecells to be accessed by using the method shown in the above embodimentsor examples. For example, the cell selecting device 1604 may determinewhether the component carriers corresponding to all the neighbor cellsbelonging to the destination base station are provided in the samefrequency band, if yes, select all the neighbor cells belonging to thedestination base station as the cells to be accessed, otherwise, selectone or more from all the neighbor cells belonging to the destinationbase station, as the cells to be accessed.

In another particular example, the apparatus 1600 may further includethe priority determining device 1402 as described above with referenceto FIG. 14, the function of which is similar to that described above andthe description of which is not repeated.

Some embodiments of the invention provide methods of cell handover underCA supporting scenarios. These methods may include the flows of cellhandover performed by the terminal device and the source base station inthe above and below embodiments or examples, the description of which isnot repeated.

Some embodiments of the invention provide a communication systemincluding the terminal device and/or the base station described in theabove and below embodiments or examples.

FIG. 17, FIG. 18, and FIG. 19 each show an application scenario to whichthe above methods of cell handover may be applied. In the figures,A01-A03, B01-B03, and C01-A03 respectively represent base stations. InFIG. 17, the coverages of the cells corresponding to the componentcarriers F_(A1) and F_(A2) are substantially overlapped with each other,and can provide similar coverages. F_(A1) and F_(A2) are in the samefrequency bands, which belongs to the typical consecutive carrieraggregation manner. FIG. 18 and FIG. 19 respectively correspond tonon-consecutive CA scenarios, in which the component carriers F_(B1) andF_(B2) are in different frequency bands, and F_(C1) and F_(C2) also arein different frequency bands. The cell corresponding to F_(B1) or F_(C1)is mainly used to ensure coverage and the cell corresponding to F_(B2)or F_(C2) is mainly used to improve throughput. The difference betweenFIG. 18 and FIG. 19 lies in that, in FIG. 19 the antenna of the cellcorresponding to F_(C2) is directed to the edge region of the cellcorresponding to F_(C1), such that the application scenario in FIG. 19can significantly improve the throughput at the edge region of the cellcorresponding to F_(C1).

According to some examples, the process of cell handover may include apreparation stage, a performing stage and a finishing stage. Differentscenarios correspond to different handover policies. The processes ofcell handover in the 3 typical application scenarios are described below

Scenario Shown in FIG. 17:

Preparation Stage:

When the terminal device is at the edge of the coverage of the currentlyserving cell, it needs to measure all the neighbor cells. A carrierfrequency corresponds to a neighbor cell, if the neighbor cellsbelonging to the same base station are in the same frequency band; onlyone neighbor cell is selected and measured. At this time, it is supposedthat the measurement result obtained by the terminal device for the cellcorresponding to F_(A1) is denoted as M_(f1), the measurement result forthe cell corresponding to F_(A2) is denoted as M_(f2), and themeasurement result for a neighbor cell is denoted as M_(f). If one ofthe following conditions is met, the terminal device transmits themeasurement result to the base station.M_(f)≧Th₁ OrM _(f) ≧M _(f1) +Th ₂ Or M _(f) ≧M _(f2) +Th ₂

That is, if the measurement result of the neighbor cell is higher than athreshold (Th₁) or is better than the measurement result of a cell towhich the terminal device is connected to, the terminal device transmitsthe measurement result to the base station. That is, the neighbor cellcan be used as a candidate destination cell.

In actual processing, the base station or the terminal device mayrandomly specify one of the cells to which the terminal device isconnected, as the object to be compared with the measurement result ofthe neighbor cell.

Performing Stage:

In this stage the destination base station and the cells to be accessedare determined. Since the carrier frequencies of candidate cellsbelonging to the same base station are in the same frequency band, thepriority of the base station can be decided by the weighted performancesof these candidate cells. The base station having the highest priorityis selected as the destination base station. Since the carrierfrequencies of candidate cells belonging to the destination base stationare in the same frequency band, all the candidate cells are used as thecells to be accessed. Here, it is supposed that the cells correspondingto F_(A1) and F_(A2) in the base station A02 are selected as the cellsto be accessed.

Finishing Stage:

The terminal device connects to a plurality of cells before handover,the number of the selected cells to be accessed is more than one and thecomponent carriers corresponding to these cells to be accessed are inthe same frequency band. When sending a handover request, the sourcebase station sends the information of all the cells to be accessed tothe destination base station.

The destination base station performs an access control estimation basedon the received information, and if it allows the terminal device toaccess, it sends an ACK message to the source base station.

After receiving the ACK message, the source base station transmits anRRC connection reconfigure message containing the mobility controlinformation, to initiate the RRC connection reconfigure for all thecells to be accessed.

When the reconfigure is completed, the terminal device chooses todisconnect from the one or more original cells, and keeps incommunication with at least one original cell, and sends asynchronization request to all the cells to be accessed to thedestination base station, so as to be synchronized to the new cells.

When the terminal device is synchronized with all the cells to beaccessed in the destination base station and completes the correspondingaccessing processes so that it is ready for data transmission, theterminal device disconnects from the original cell and is completelyserved by the new base station and cells.

Scenario Shown in FIG. 18:

Preparation Stage:

when the terminal device is at the edge of a cell, it needs to measureall the neighbor cells, one of which corresponds to a carrier frequency.At this time, it is supposed that the measurement result of the terminaldevice for the cell corresponding to F_(B1) is denoted as M_(f1), themeasurement result for the cell corresponding to F_(B2) is denoted asM_(f2), and the measurement result for a neighbor cell is denoted asM_(f). If one of the following conditions is met, the terminal devicetransmits the measurement result of the neighbor cell to the basestation:M_(f)≧Th₁, orM _(f) ≧M _(f1) +Th ₂ Or M _(f) ≧M _(f2) +Th ₂

That is, if the measurement result of the neighbor cell is higher than athreshold (Th₁) or is better than the measurement result of any cell towhich the terminal device is connected to, the terminal device transmitsthe measurement result of the neighbor cell to the base station. Thatis, the neighbor cell is selected as a candidate cell for handover.

In actual processing, the base station or the terminal device mayrandomly specify one of the cells to which the terminal device isconnected, as the object to be compared with the measurement result ofthe neighbor cell.

Performing Stage:

In this stage the destination base station and the cells to be accessedare determined. The priority of the candidate base station can bedecided depending upon whether or not the carrier frequencies ofcandidate cells belonging to the same base station are in the samefrequency band. The base station having the highest priority is selectedas the destination base station. The cells to be accessed are decidedbased on the number of candidate cells belonging to the destination basestation, whether or not in the same frequency band, and the relationshipwith the carrier frequency before handover. Here it is supposed that thecells corresponding to F_(B1) and F_(B2) in the base station B03 areselected as the cells to be accessed.

Finishing Stage:

It is supposed that the terminal device is connected to only one cellbefore handover. The number of the cells to be accessed is more thanone, and the component carriers corresponding to these cells to beaccessed are in different frequency bands. It is also supposed thatF_(B1) refers to the frequency of the cell before the handover. At thistime, the cell corresponding to F_(B1) is selected as the primary cellto be accessed, and when sending the handover request, the source basestation sends the information of the primary cell to the destinationbase station.

The destination base station performs access control estimation, and ifit allows the terminal device to access, it sends an ACK message to thesource base station.

After receiving the ACK message, the source base station transmits anRRC connection reconfigure message containing the mobility controlinformation, to initiate the RRC connection reconfigure for the primarycell to be accessed.

When the reconfigure is completed, the terminal device chooses todisconnect from the original cell, and send a synchronization request tothe primary cell to be accessed to the destination base station, so asto be synchronized to the new cells.

When the terminal device is synchronized with the primary cell to beaccessed in the destination base station and completes the correspondingaccessing processes, it is ready for data transmission. At this time,the terminal device is completely served by the new base station andcells.

The terminal device initiates an RRC connection reconfigure messageexcluding the mobility control information, to add the component carrierF_(B2), and to access the cell corresponding to F_(B2). In this waycarrier aggregation is realized.

Scenario Shown in FIG. 19:

Preparation Stage:

When the terminal device is at the edge of a cell, it needs to measureall the neighbor cells, one of which corresponds to a carrier frequency.At this time, it is supposed that the measurement result of the terminaldevice for the cell corresponding to F_(C1) is denoted as M_(f1), themeasurement result for the cell corresponding to F_(C2) is denoted asM_(f2), and the measurement result for a neighbor cell is denoted asM_(f). If one of the following conditions is met, the terminal devicetransmits the measurement result of the neighbor cell to the basestation:M_(f)≧Th₁, orM _(f) ≧M _(f1) +Th ₂ And M _(f) ≧M _(f2) +Th ₂

That is, if the measurement result of the neighbor cell is higher than athreshold (Th₁) or is better than the measurement results of all thecells to which the terminal device is connected to, the terminal devicetransmits the measurement result of the neighbor cell to the basestation. That is, the neighbor cell is selected as a candidate cell forhandover.

In actual processing, the base station or the terminal device selectsone cell having the best measurement result, as the object to becompared with the measurement result of the neighbor cell.

Performing Stage:

In this stage the destination base station and the cells to be accessedare determined. Particularly, the priority of the candidate base stationcan be decided depending upon whether or not the carrier frequencies ofcandidate cells belonging to the same base station are in the samefrequency band. The base station having the highest priority is selectedas the destination base station. The cells to be accessed are decidedbased on the number of candidate cells belonging to the destination basestation, whether or not in the same frequency band, and the relationshipwith the carrier frequency before handover. Here it is supposed that thecells corresponding to F_(C1) and F_(C2) in the base station C03 areselected as the cells to be accessed.

Finishing Stage:

It is supposed that the terminal device connects to a plurality of cellsat the same time before handover, the number of the selected cells to beaccessed is more than one and the component carriers corresponding tothese cells to be accessed are in different frequency bands. Whensending a handover request, the source base station sends theinformation of all the cells to be accessed to the destination basestation.

The destination base station performs access control estimation, and ifit allows the terminal device to access, it sends an ACK message to thesource base station.

After receiving the ACK message, the source base station transmits anRRC connection reconfigure message containing the mobility controlinformation, to initiate the RRC connection reconfigure for all thecells to be accessed.

When the reconfigure is completed, the terminal device chooses todisconnect from one or more original cells, and keeps in communicationwith at least one original cell, and sends a synchronization request toall the cells to be accessed to the destination base station, so as tobe synchronized to the new cells.

When the terminal device is synchronized with all the cells to beaccessed in the destination base station and completes the correspondingaccessing processes so that it is ready for data transmission, theterminal device disconnects from the original cell and is completelyserved by the new base station and cells.

It should be understood that the above embodiments and examples areillustrative, rather than exhaustive. The present disclosure should notbe regarded as being limited to any particular embodiments or examplesstated above.

As an example, the components, units or steps in the above apparatusesand methods can be configured with software, hardware, firmware or anycombination thereof in the base station or the terminal device in acommunication network, as part of the base station or the terminaldevice, by using method or means well known in the art, the details ofwhich are omitted herein. As an example, the above methods or apparatuscan be realized in existing base station or terminal device in acommunication system, with a modification to the related parts of theexisting base station or terminal device.

As an example, in the case of using software or firmware, programsconstituting the software for realizing the above method or apparatuscan be installed to a computer with a specialized hardware structure(e.g. the general purposed computer as shown in FIG. 21) from a storagemedium or a network. The computer, when installed with various programs,is capable of carrying out various functions.

In FIG. 21, a central processing unit (CPU) 2101 executes various typesof processing in accordance with programs stored in a read-only memory(ROM) 2102, or programs loaded from a storage unit 2108 into a randomaccess memory (RAM) 2103. The RAM 2103 also stores the data required forthe CPU 2101 to execute various types of processing, as required. TheCPU 2101, the ROM 2102, and the RAM 2103 are connected to one anotherthrough a bus 2104. The bus 2104 also connects to an input/outputinterface 2105.

The input/output interface 2105 connects to an input unit 2106 composedof a keyboard, a mouse, etc., an output unit 2107 composed of a cathoderay tube or a liquid crystal display, a speaker, etc., the storage unit2108, which includes a hard disk, and a communication unit 2109 composedof a modem, a terminal adapter, etc. The communication unit 2109performs communicating processing. A drive 2110 is connected to theinput/output interface 2105, if needed. In the drive 2110, for example,removable media 2111 is loaded as a recording medium containing aprogram of the present invention. The program is read from the removablemedia 2111 and is installed into the storage unit 2108, as required.

In the case of using software to realize the above consecutiveprocessing, the programs constituting the software may be installed froma network such as Internet or a storage medium such as the removablemedia 2111.

Those skilled in the art should understand the storage medium is notlimited to the removable media 2111, such as, a magnetic disk (includingflexible disc), an optical disc (including compact-disc ROM (CD-ROM) anddigital versatile disk (DVD)), an magneto-optical disc (including an MD(Mini-Disc) (registered trademark)), or a semiconductor memory, in whichthe program is recorded and which are distributed to deliver the programto the user aside from a main body of a device, or the ROM 2102 or thehard disc involved in the storage unit 2108, where the program isrecorded and which are previously mounted on the main body of the deviceand delivered to the user.

The present disclosure further provides a program product havingmachine-readable instruction codes which, when being executed, may carryout the method for cross phase modulation recovery according to theembodiments.

Accordingly, the storage medium for bearing the program product havingthe machine-readable instruction codes is also included in thedisclosure. The storage medium includes but not limited to a flexibledisk, an optical disc, a magneto-optical disc, a storage card, or amemory stick, or the like.

In the above description of the embodiments, features described or shownwith respect to one embodiment may be used in one or more otherembodiments in a similar or same manner, or may be combined with thefeatures of the other embodiments, or may be used to replace thefeatures of the other embodiments.

As used herein, the terms the terms “comprise,” “include,” “have” andany variations thereof, are intended to cover a non-exclusive inclusion,such that a process, method, article, or apparatus that comprises a listof elements is not necessarily limited to those elements, but mayinclude other elements not expressly listed or inherent to such process,method, article, or apparatus.

Further, in the disclosure the methods are not limited to a processperformed in temporal sequence according to the order described therein,instead, they can be executed in other temporal sequence, or be executedin parallel or separatively. That is, the executing orders describedabove should not be regarded as limiting the method thereto.

While some embodiments and examples have been disclosed above, it shouldbe noted that these embodiments and examples are only used to illustratethe present disclosure but not to limit the present disclosure. Variousmodifications, improvements and equivalents can be made by those skilledin the art without departing from the scope of the present disclosure.Such modifications, improvements and equivalents should also be regardedas being covered by the protection scope of the present disclosure.

What is claimed is:
 1. A method for cell handover in a communicationsystem supporting carrier aggregation, comprising: judging, by a sourcebase station in the communication system, whether component carrierscorresponding to one or more cells to be accessed which belong to adestination base station selected for a terminal device are in a samefrequency band, wherein the terminal device is currently served by thesource base station and is to be handed over, and if yes, packagingconfiguration information of all the one or more cells to be accessed ina handover command for initiating cell handover, otherwise, packagingconfiguration information of one or more of the one or more cells to beaccessed in the handover command; and transmitting the handover commandto the destination base station.
 2. The method for cell handover in acommunication system of claim 1, further comprising: selecting one cellfrom the one or more cells to be accessed, as a primary cell to beaccessed, and wherein packaging the configuration information of one ormore of the one or more cells to be accessed in the handover commandcomprises: packaging configuration information of the primary cell to beaccessed in the handover command.
 3. The method for cell handover in acommunication system of claim 2, wherein selecting one cell from the oneor more cells to be accessed as the primary cell to be accessedcomprises: judging whether there is a cell, among the one or more cellsto be accessed, component carriers of which are in a same frequency bandwith those corresponding to a currently serving cell of the terminaldevice; and if yes, selecting the cell as the primary cell to beaccessed, otherwise, selecting one cell having best performance amongthe one or more cells to be accessed, as the primary cell to beaccessed.
 4. The method for cell handover in a communication system ofclaim 2, wherein selecting one cell from the one or more cells to beaccessed as the primary cell to be accessed comprises: selecting onecell having best performance among the one or more cells to be accessed,as the primary cell to be accessed.
 5. The method for cell handover in acommunication system of claim 1, wherein if the terminal device iscurrently connected to a plurality of cells of the source base station,the terminal device keeps in communication with one of the plurality ofcells of the source base station before being handed over to thedestination base station.
 6. The method for cell handover in acommunication system of claim 1, further comprising: selecting, by thesource base station based on a performance measurement report for one ormore neighbor cells of the terminal device transmitted from the terminaldevice, a candidate base station from one or more candidate basestations corresponding to the one or more neighbor cells, as thedestination base station; and selecting one or more cells from all cellsbelonging to the destination base station in the one or more neighborcells, as the one or more cells to be assessed for the terminal device.7. The method for cell handover in a communication system of claim 6,wherein selecting a candidate base station from one or more candidatebase stations as the destination base station comprising: selecting analgorithm suitable for carrier aggregation manners of the one or morecandidate base stations to calculate priorities of the one or morecandidate base stations, based on the performance measurement report andbased on the carrier aggregation manners of the one or more candidatebase stations; and selecting one candidate base station having a highestpriority from the one or more candidate base stations, as thedestination base station.
 8. The method for cell handover in acommunication system of claim 7, wherein calculating priorities of theone or more candidate base stations comprises: judging whether componentcarriers corresponding to all neighbor cells belonging to a samecandidate base station in the one or more neighbor cells are in a samefrequency band; and if yes, calculating priority of the candidate basestation according to performances of all the neighbor cells belonging tothe candidate base station, otherwise, calculating the priority of thecandidate base station according to performance one having bestperformance of all the neighbor cells belonging to the candidate basestation.
 9. The method for cell handover in a communication system ofclaim 8, wherein calculating the priority of the candidate base stationaccording to the performances of all the neighbor cells belonging to thecandidate base station comprises: calculating a sum of the performancesor weighted performances of all the neighbor cells belonging to thecandidate base station based on the performance measurement report, asthe priority of the candidate base station.
 10. An apparatus for cellhandover, configured in a base station of a communication systemsupporting carrier aggregation, and comprising: a command forming deviceconfigured to judge, whether component carriers corresponding to one ormore cells to be accessed which belong to a destination base stationselected for a terminal device are in a same frequency band, wherein theterminal device is currently served by the base station and is to behanded over, and if yes, package configuration information of all theone or more cells to be accessed in a handover command for initiatingcell handover, otherwise, package configuration information of one ormore of the one or more cells to be accessed in the handover command;and a transmitting device configured to transmit the handover command tothe destination base station.
 11. The apparatus for cell handover ofclaim 10, further comprising: a primary cell selecting device configuredto select one cell from the one or more cells to be accessed, as aprimary cell to be accessed.
 12. The apparatus for cell handover ofclaim 11, wherein the primary cell selecting device is configured to:judge whether there is a cell, among the one or more cells to beaccessed, component carriers of which are in a same frequency band withthose corresponding to a currently serving cell of the terminal device;and if yes, select the cell as the primary cell to be accessed,otherwise, select one cell having best performance among the one or morecells to be accessed, as the primary cell to be accessed.
 13. Theapparatus for cell handover of claim 11, wherein the primary cellselecting device is configured to: select one cell having bestperformance among the one or more cells to be accessed, as the primarycell to be accessed.
 14. The apparatus for cell handover of claim 10,wherein if the terminal device is currently connected to a plurality ofcells of the base station, the terminal device keeps in communicationwith one of the plurality of cells of the base station before beinghanded over to the destination base station.
 15. The apparatus for cellhandover of claim 10, further comprising: a receiving device configuredto a performance measurement report for one or more neighbor cells ofthe terminal device transmitted from the terminal device; a destinationbase station selecting device configured to select, based on theperformance measurement report, a candidate base station from one ormore candidate base stations corresponding to the one or more neighborcells, as the destination base station; and a cell selecting deviceconfigured to select one or more cells from all cells belonging to thedestination base station in the one or more neighbor cells, as the oneor more cells to be assessed for the terminal device.
 16. The apparatusfor cell handover of claim 15, further comprising: a prioritydetermining device configured to select an algorithm suitable forcarrier aggregation manners of the one or more candidate base stationsto calculate priorities of the one or more candidate base stations,based on the performance measurement report and based on the carrieraggregation manners of the one or more candidate base stations; andwherein the destination base station is configured to select onecandidate base station having a highest priority from the one or morecandidate base stations, as the destination base station.
 17. Theapparatus for cell handover of claim 16, wherein the prioritydetermining device is configured to calculate priorities of the one ormore candidate base stations by: judging whether component carrierscorresponding to all neighbor cells belonging to a same candidate basestation in the one or more neighbor cells are in a same frequency band;and if yes, calculating priority of the candidate base station accordingto performances of all the neighbor cells belonging to the candidatebase station, otherwise, calculating the priority of the candidate basestation according to performance one having best performance of all theneighbor cells belonging to the candidate base station.
 18. Theapparatus for cell handover of claim 17, wherein the prioritydetermining device is configured to: calculate a sum of the performancesor weighted performances of all the neighbor cells belonging to thecandidate base station based on the performance measurement report, asthe priority of the candidate base station.
 19. A base station in acommunication system supporting carrier aggregation, comprising anapparatus for cell handover comprising: a command forming deviceconfigured to judge, whether component carriers corresponding to one ormore cells to be accessed which belong to a destination base stationselected for a terminal device are in a same frequency band, wherein theterminal device is currently served by the base station and is to behanded over, and if yes, package configuration information of all theone or more cells to be accessed in a handover command for initiatingcell handover, otherwise, package configuration information of one ormore of the one or more cells to be accessed in the handover command;and a transmitting device configured to transmit the handover command tothe destination base station.
 20. A non-transitory computer-readablestorage medium, which stores therein a computer program which, whenexecuted by a computer, causes the computer to execute a method for cellhandover in a communication system supporting carrier aggregation, themethod comprising: judging, by a source base station in thecommunication system, whether component carriers corresponding to one ormore cells to be accessed which belong to a destination base stationselected for a terminal device are in a same frequency band, wherein theterminal device is currently served by the source base station and is tobe handed over, and if yes, packaging configuration information of allthe one or more cells to be accessed in a handover command forinitiating cell handover, otherwise, packaging configuration informationof one or more of the one or more cells to be accessed in the handovercommand; and transmitting the handover command to the destination basestation.